Aminoglycoside Hartford Nomogram Calculator (Once-Daily Dosing)

Clinical Guide: Once-Daily Aminoglycosides and the Hartford Nomogram

Traditionally, aminoglycosides like Gentamicin and Tobramycin were administered in multiple small doses throughout the day. However, modern pharmacology favors **extended-interval aminoglycoside dosing (EIAD)**—commonly known as once-daily dosing.

EIAD capitalizes on two key pharmacodynamic traits of aminoglycosides: **concentration-dependent killing** (higher peaks maximize bacterial eradication) and the **post-antibiotic effect (PAE)**, where bacterial growth remains suppressed even after serum drug levels drop below the minimum inhibitory concentration.

How the Hartford Nomogram Protocol Works

The Hartford Nomogram applies specifically to a standardized initiation dose of 7 mg/kg of either Gentamicin or Tobramycin. To use the tool accurately in an acute care setting, clinicians follow these exact tracking steps:

1. Initiate an intravenous infusion of 7 mg/kg of the selected aminoglycoside.
2. Draw a single random serum drug concentration profile exactly 6 to 14 hours following the start of that initial infusion.
3. Plot the serum level alongside the timing marker onto the nomogram coordinate grid matrix to establish the safest subsequent dosing frequency.

Interpreting the Dosing Interval Windows

The grid splits the tracking results into three actionable clearance performance columns, plus a critical safety off-scale zone:

• q24h Window: Patient shows strong, rapid clearance. The drug clears efficiently enough to support regular daily execution cycles.
• q36h / q48h Windows: Patient shows mild-to-moderate delayed clearance. Extending the dosing cycle allows tissue thresholds to fall to safe levels before adding more drug, preventing accumulation.
• Off-Nomogram (Toxic Overload): Patient clearance has essentially stalled. Extended dosing protocols must be abandoned immediately to prevent severe, irreversible ototoxicity and acute tubular necrosis (nephrotoxicity).